1. Field of the Invention
The present invention relates to a printing method and a printing apparatus for developing a latent image on the surface of a photo-conductor drum using liquid toner, to a control device and a control method for controlling a laser output of the printing device, and to a resister control device of the printing device.
2. Description of the Related Art
Heretofore, wet-type electro photographic printing apparatuses have been known in the art, which is provided for forming an image on the surface of a photoconductor drum being rotated at a constant speed by successively overlaying colors such as yellow (Y), magenta (M), cyan (C), and black (K) and then transferring an image formed by overlaying one image on another using a plurality of different color liquid toners onto a sheet of printing paper placed between a transfer roller and a backup roller through the transfer roller. The printing apparatus comprises: charging means for charging the surface of a photoconductor drum having a photosensitivity; exposing means for performing an exposure scan on the photoconductor drum on the basis of drawing data to form a latent image on the photoconductor drum; and developing means for developing the latent image on the photoconductor drum. The developing means includes a plurality of developing rollers that sequentially supply liquid toners of multiple colors on the photoconductor drum.
Furthermore, the exposing means includes a laser-emitting source, a polygon scanner, or the like. A laser beam emitted from the laser-emitting source is incident on the polygon scanner being rotated at a predetermined speed and is then reflected from the polygon scanner. Subsequently, the reflected laser beam passes through an fxcex8 lens and scans the surface of the photoconductor drum to make a latent image.
Conventionally, such a kind of printing apparatus performs the following process.
First, the charging device charges the surface of the photoconductor drum on the basis of an image data. Then, the exposing device forms a latent image on the surface of the photoconductor drum on the basis of a drawing data. Subsequently, the latent image is developed by liquid toner to make an image.
The development with liquid toner is performed by bringing a developing roller partially dipping in the liquid toner close to the photoconductor drum and then revolving it around its axis. On this occasion, meniscus is formed in a comparatively narrow space between the developing roller and the photoconductor drum because the surface of the liquid turner in the space wets them and is provided as a bridge between them. Then, a potential difference is applied on between the exposed surface portion and the remaining surface portion on the photoconductor and the developing roller to permit the electrophoresis movement of liquid toner in the meniscus. As a result, the liquid toner is supplied from the developing roller to the photoconductor roller.
Subsequently, the image formed on the surface of the photoconductor drum is transferred to the surface of a transfer roller. Then, a sheet of printing paper is fed between the transfer roller having the transferred image and the backup roller. Consequently, the image on the transfer roller is transferred on the surface of the printing paper while the paper passes through between the rollers.
In the case of forming an image on the photoconductor drum by supplying liquid toner from the developing roller to the photoconductor drum, an excess amount of the liquid toner may be supplied as a result of capillary phenomenon when the distance between the developing roller and the photoconductor roller becomes closer than the predetermined distance, resulting in an indistinct image. On the other hand, if these rollers are located too far from each other, poor meniscus of the liquid toner can be formed between the rollers. As a result, the liquid toner cannot be transferred from the developing roller to the photoconductor drum, so that the image formation cannot be performed. On the other hand, there are various kinds of customers"" needs for printed materials to be obtained by the printing apparatus constructed as described above, such as for different sizes (e.g., A1-, A2-, and B1-sizes) and thicknesses of sheets of printing paper. For printing a multi-color image, in most cases, all of two or more colors to be required are stacked on the same place one after another and a thickness of one area on the recording medium may become different from that of another area depending on the number of colors being stacked on each area. Therefore, printing conditions including the rotation speed of photoconductor drum, the rotation speed of developing roller, the properties of liquid toner, and so on should be adjusted to obtain an appropriate distance between the developing roller and the photoconductor roller for allowing the most clear image every time the customer performs a printing using liquid toner and recording medium which are different from those used in the latest printing.
Conventionally, however, the developing roller and the photoconductor have been kept at a constant distance from each other on the basis of the operator""s practical experience and guesswork, so that the resulting image may be subtly deferent from one previously printed every time the image is printed under the different conditions, causing a problem of an undesired effect on the image quality.
Therefore one of the objects of the present invention is to provide a printing apparatus that keeps an excellent image quality by avoiding an influence upon an image to be exerted by the image formation on the surface of photoconductor drum using liquid toner.
In the case of forming an image on the photoconductor drum in an image-on-image fashion, on the other hand, an image development can be performed by causing the migration of charged toner particles when the potential of an area exposed by a beam of laser (i.e., an area on which electrostatic latent image is formed) becomes less than the potential of the developing roller with respect to the potential of charged photoconductor drum. For example, a laser-exposure potential to be defined by the sensitivity for a laser wavelength can be obtained on the surface of photoconductor drum for an image formation of a first color. At the time of forming an image of second color, a laser-exposure potential to be defined by the sensitivity for a laser wavelength can be obtained on another part of the surface of photoconductor drum, which is not exposed in the step of first color, for an image formation of a second color. In this case, however, if the second color is applied on the same area as that of the first color, there is a possibility that a desired laser exposure potential cannot be attained because of the presence of first-color toner on that area. The existing toner absorbs or reflects laser energies, so that the desired laser exposure potential cannot be obtained when the laser""s output power is not adjusted. As a result, it becomes difficult to obtain a clear image, causing a problem of an undesired effect on the image quality.
Furthermore, for adjusting the output of laser, a data for each color as a part of output data of laser should be kept to define an output data for printing such a color. Here, if the resolution of the laser output is 256 levels of gradation, for example, 8 bits of data can be required for one dot (one pixel). Therefore, for example, for successively stacking eight colors (e.g., yellow and so on) on an area corresponding to one pixel, 64 bits of data (i.e., 8 bitsxc3x978 colors=64 bits) per pixel is required. Thus, the more the size of an image to be printed is increased or the more the resolution increases, the more space for storing laser output data in the large storing device is required.
Therefore, another object of the present invention is to provide a laser-output control device and a method for controlling a laser output, where a clear image can be obtained by controlling a laser power such that the laser power is appropriately adjusted under the conditions of stacking colors on the same image-forming area, or under the conditions of without stacking colors.
A still another embodiment of the present invention is to provide a laser-output control device to be equipped in a wet type electro photographic printing apparatus for allowing the reduction in the capacity of the recording device that stores laser output data, and is also to provide a method for controlling the laser output.
In the above printing apparatus, furthermore, the photoconductor drum and a polygon scanner of exposure means are capable of rotating at a constant speed respectively in isolation from each other. Therefore, there is a possibility of causing out-of-register colors, i.e., a second or later color cannot be positioned properly on an initial position of image formation, which is a position for starting a scanning movement of the polygon scanner on the surface of the photoconductor drum, resulting in an unclear image. In this case, therefore, there is a problem in which a high-quality printed material cannot be obtained.
Another object of the present invention is to provide a resister control device of a printing apparatus for obtaining a high-quality printed material by maintaining register of each color to a high degree when a multi-color image is formed on the surface of a photoconductor drum using liquid toner
In the conventional printing method, liquid toner is supplied to the surface of a photoconductor drum by permitting a rotational movement of a developing toner at a const speed. Thus, it is difficult to promptly make meniscus of the liquid toner between the surface of the developing roller and the surface of the photoconductor roller at the time of liquid-toner supply by making them close to each other. In particular, in the case of a multi-color printing using liquid toners of four different colors, there is a possibility of slightly sifting the time of forming meniscus at the time of starting a development for each color from its predetermined time. Such a time lag causes an unstable image development, so that there is a possibility that the decrease in printing quality may be caused as the resulting image may be unclear.
Therefore, another object of the present invention is to provide a printing method and a printing apparatus that improve the quality of printing.
An first aspect of the present invention is a printing apparatus, comprising a photoconductive drum having a surface on which an image is formed; a charging means or charging the surface of the photoconductive drum; an exposure means for preparing an electrostatic latent image by exposing the surface of the photoconductor drum after the charging with the charging means; a developing means for developing the electrostatic latent image by supplying liquid toner on the surface of the photoconductor by electrophoresis after the exposure with the exposure means; a transfer roller for receiving the image after the development with the developing means; a backup roller for transferring the image from the transfer means to a printing paper; and a control means for controlling the charging means, the exposure means, the developing means, the transfer roller, and the backup roller, where the developing means includes a main body of an developing device for storing the liquid toner and developing rollers mounted on the main body and supplies the liquid toner to the photoconductor drum to allow the development, and a distance between the surface of the developing roller and the surface of the photoconductor drum is adjustable.
According to this invention, the distance between the surface of each of the first, second, third, and fourth developing rollers and the surface of the photoconductor drum can be adjustable, so that the distance can be appropriately defined for various kinds of printing movements, depending on the rotation speeds of the photoconductor roller and developing rollers, the properties of liquid toner. Consequently, the liquid toner can be supplied with an appropriate distance that allows the formation of a clear image, so that an image with an excellent quality can be maintained while avoiding an influence upon an image.
In the printing apparatus of the present invention, preferably, a main body of the developing device has a plurality of toner storage chambers for storing liquid toners corresponding to a plurality of printing colors, and each of the developing rollers is arranged in each of the toner storage chambers.
According to this invention, liquid toner of each color to be printed can be stored in one of the toner storage chamber and the developing rollers are provided for the respective chambers, so that multi-color printing can be performed without causing undesired mixing of colors, adapting to better meet various customers"" needs.
In the printing apparatus of the present invention, preferably, the photoconductor drum has a drawing area on which a drawing is performed and a non-drawing area on which a drawing is not performed; and the transfer roller has a drawing area on which a drawing is performed and a non-drawing area on which a drawing is not performed, where a diameter of the photoconductor drum is equal to a diameter of the transfer roller, and movements of the main body of the developing device and the developing roller for a predetermined printing color selected from the plurality of the printing color is performed within the non-drawing area of the photoconductor drum.
According to this invention, using the non-drawing area, the main body of the developing device and the developing rollers shift their positions, so that their movements do not affect on the drawing. Therefore, the drawing movement can be smoothly and rapidly shifted from one color to the next color. The drawing area and the non-drawing area are present, so that it is possible to adapt to the various sizes of the printing paper as the range of the non-drawing area can be varied if required. Therefore, the printing apparatus having one photoconductor drum and one transfer roller is capable of printing on various kinds of printing paper, so that the manufacture and arrangement of the photoconductor drum or the like can be easily performed.
In the printing apparatus of the present invention, preferably, the transfer roller is formed so as to be attachable/detachable to the photoconductor drum and the backup roller is formed so as to be attachable/detachable to the transfer roller, where the transfer roller is being detached from the photoconductor drum until the development of the photoconductor drum by the developing means is completed, while the backup roller is being detached from the transfer roller until the printing paper is placed between the backup roller and the transfer roller.
According to this invention, the development of multi-color printing on the surface of the photoconductor drum 2 can be performed without any obstruction and the backup roller 21 does not obstruct the paper feed, so that the printing can be performed smoothly.
In the printing apparatus of the present invention, preferably, the photoconductor drum, the transfer roller, and the backup roller perform their respective rotary motions under the controls of the control means such that their phases are synchronized with each other.
According to this invention, the transfer roller, and the backup roller can be rotated with their phases in synchronism with each other under the controls of the control means, respectively. Therefore, there is no displacement of drawing positions, so that a high-quality printing can be attained.
In the printing apparatus of the present invention, preferably, each of the developing rollers being arranged in each of the plurality of toner storage chambers is independently capable of adjusting a distance from the photoconductor drum.
According to this invention, each of the first, second, third, and fourth developing rollers individually mounted on the respective toner storage chambers is capable of independently adjusting the distance with the photoconductor drum 2, so that it is possible to absorb errors in the manufacture of each developing roller and errors in the installation. Therefore, each of the developing rollers is able to keep the distance at a constant, so that the high quality printing can be attained.
A second aspect of the present invention is a laser output control device to be used in a wet-type electrophotographic printing apparatus having a photoconductor drum with a surface on which an image is formed, a charging means for charging the surface of the photoconductor drum, an exposure means for preparing an electrostatic latent image by irradiating a laser beam on the surface of the photoconductor drum, and a developing means for developing the electrostatic latent image on the surface of the photoconductor drum by stacking a plurality of colors thereon, comprising: a laser output data memory part for storing laser output data for each color of every combination of the plurality of colors; a color combination data memory part for storing drawing data as color combination data for each of pixels; a laser control part for controlling the laser beam by selecting laser output data corresponding to a color to be drawn, wherein the laser control part selects the color to be drawn from the color combination data in the color combination data memory part, selects a pixel including the color to be drawn, selects a pixel having the same color combination as that of the selected pixel from the laser output data memory part, together with selecting the same color as the color to be drawn from the pixel, and provides the laser output data corresponding to the selected color as laser output data of the color to be drawn.
According to this invention, the output level of laser for drawing color from the laser output control device allows the selection of color to be drawn from the color combination data and the selection of pixel in which color to be draw is incorporated. A pixel having color corresponding to the selected pixel is selected from the laser output data memory part and is then provided as laser output data of color to be drawn, so that the power of laser can be varied depending on whether colors are stacked one after another or not, or depending on the other conditions. Consequently, a clear image can be obtained. In addition, the output level of color to be drawn may be defined with reference to the laser output memory part. The laser output data corresponds to drawing data of color combinations in which drawing data is prepared for each pixel. Therefore, for example, there is no need to provide 8 bits of data for one dot to be required in 256 levels of gradation. Therefore, the capacity of the recording device for storing laser output data can be reduced.
In the laser output control device of the present invention, preferably, the plurality of colors includes at least two colors.
According to this invention, a multi-color printing can be attained, so that it will adapt to better meet various customers"" needs.
A third aspect of the present invention is to a method of laser output control in a wet-type electro photographic printing apparatus having a photoconductor drum with a surface on which an image is formed, a charging means for charging the surface of the photoconductor drum, an exposure means for preparing an electrostatic latent image by irradiating a laser beam on the surface of the photoconductor drum, and a developing means for developing the electrostatic latent image on the surface of the photoconductor drum by stacking a plurality of colors thereon, where the laser beam is controlled by a laser control part, comprising the steps of: storing laser output data for each color of every combination of the plurality of colors in a laser output data memory part; storing drawing data as color combination data for each of pixels in a color combination data memory part; selecting the color to be drawn from the color combination data in the color combination data memory part by the laser control part; selecting a pixel having the same color combination as that of the selected pixel from the laser output data memory part, together with selecting the same color as the color to be drawn from the pixel; and providing the laser output data corresponding to the selected color as laser output data of the color to be drawn.
According to this invention, just as in the case of the above laser output control device, laser power can be varied depending on whether colors are stacked or not or depending on the change in conditions. Thus, the capacity of the recording device for storing laser output data can be reduced.
A fourth aspect of the present invention is a printing register control device having a photoconductor drum with a surface on which an image is formed, a charging means for charging the surface of the photoconductor drum; an exposure means for preparing an electrostatic latent image by drawing with an exposure scanning on the surface of the photoconductor drum after the charging with the charging means on the basis of drawing data, a developing means for developing the electrostatic latent image on the surface of the photoconductor drum by sequentially supplying multi-color liquid toners on the surface of the photoconductor drum by electrophoresis after the exposure scanning of the exposure means, a transfer roller for receiving the image after the development with the developing means, a backup roller for transferring the image on the transfer roller to the printed paper, and a control means for controlling each of these means and each of these rollers, comprising: a drawing synchronization signal interface circuit for outputting a drawing synchronization signal to an exposure signal outputted to the exposure means; an encoder for detecting a rotation angle of the photoconductor drum; a temporary drawing trigger signal generation part for providing the exposure means with a position on which a drawing initiation trigger signal is generated, by a rotation angle detection signal outputted from the encoder; a first color initial rotation angle memory part for storing an initial rotation angle of the photoconductor drum at the time of detecting a first drawing synchronization signal outputted from the drawing synchronization signal interface circuit after the generation of a temporary drawing trigger signal for the first color; a N-th color initial rotation angle memory part for storing an initial rotation angle of the photoconductor drum at the time of detecting a first drawing synchronization signal outputted from the drawing synchronization signal interface circuit after the generation of a temporary drawing trigger signal for the second or subsequent color; a phase difference calculation part for calculating a phase difference between an initial rotation angle of the photoconductor drum stored in the first color initial rotation angle memory part and an initial rotation angle of the photoconductor drum stored in the N-th color initial rotation angle memory part; and a phase difference correction circuit for correcting the phase difference until an actual drawing initiation synchronization signal is generated on the basis of the result of calculation from the phase difference calculation part.
According to this invention, the phase difference between the initial rotation angles of the photoconductor drum stored in the first color initial rotation memory part and the N-th color initial rotation angle memory part is calculated at the phase difference calculation part. Depending on the results of such a calculation, the correction for changing the rotation speed of the photoconductor drum by the phase difference correction circuit during the time period until a synchronization signal for initiating an actual drawing is generated. Therefore, the initiation of actual drawing of fist color always corresponds to that of second or other color, so that the register of each color can be maintained at a high level when multi-color printing is performed. As a result, the printing material with a high quality can be obtained.
In this invention, preferably, the photoconductor drum is actuated by a servo motor and a feedback encoder signal from the servo motor is used together with the rotation angle detection encoder of the photoconductor drum.
According to this invention, two different functions can be attained by one encoder, so that the number of components to be used can be reduced.
In this invention, preferably, a time period from a first drawing synchronization signal after the generation of the first color temporary drawing trigger signal to a fist color actual drawing initiation synchronization signal is an integral multiple of a cycle of exposure scanning.
According to this invention, the time period from an initial synchronization signal after the generation of first color temporary drawing trigger signal to a synchronization signal of fist color actual drawing initiation is an integral multiple of a cycle of exposure scanning movement, so that there is no output of the synchronization signal of actual drawing initiation during the exposure scanning. Therefore, each color can be registered more perfectly.
A fifth aspect of the present invention is a printing method for bringing a developing roller in close to a photoconductor drum having a surface on which an electrostatic latent image is formed, and rotating the developing roller to supply liquid toner, which is supplied on the surface of the developing roller such that at least the surface of the developing roller is wet with the liquid toner, on the surface of the photoconductor drum by electrophoresis to develop the electrostatic latent image, comprising the step of: rotating the developing roller before the development of the electrostatic latent image by supplying the liquid toner, where the rotation speed of the developing roller before the development of the electrostatic latent image is faster than the rotation speed of the developing roller during the development of the electrostatic latent image.
In this invention, the developing roller is brought in close to the photoconductor drum and is rotated to supply the liquid toner supplied on the surface of the developing roller to the photoconductor drum by electrophoresis. Before the development of the electrostatic latent image by supplying the liquid toner, the rotation speed of the developing roller before the development of the electrostatic latent image is faster than the rotation speed of the developing roller during the development of the electrostatic latent image. Therefore, the amount of liquid toner to be supplied between the photoconductor drum and the developing roller becomes increased, so that meniscus can be quickly formed when the change of colors takes place, so that a stable development can be attained and the image quality can be improved.
A sixth aspect of the present invention is a printing method for bringing one of developing rollers corresponding to a color component in close to a photoconductor drum having a surface on which a plurality of electrostatic latent images is formed for every color component, and rotating the developing roller to supply liquid toner corresponding to the color component, which is supplied on the surface of the developing roller such that at least the surface of the developing roller is wet with the liquid toner, on the surface of the photoconductor drum by electrophoresis to develop the electrostatic latent image, comprising the step of: rotating the developing roller before the development of the electrostatic latent image by supplying the liquid toner, where the rotation speed of the developing roller before the development of the electrostatic latent image is faster than the rotation speed of the developing roller during the development of the electrostatic latent image.
In this invention, the developing roller corresponding to an electrostatic latent image formed for every color component is brought in close to the photoconductor drum and is rotated to supply the liquid toner supplied on the surface of the developing roller to the photoconductor drum by electrophoresis. Before the development of the electrostatic latent image by supplying the liquid toner, the rotation speed of the developing roller before the development of the electrostatic latent image is faster than the rotation speed of the developing roller during the development of the electrostatic latent image. After passing the predetermined time period, then the developing roller is decelerated to the rotation speed thereof at the time of development. Therefore, if another developing roller is brought in close to the photoconductor drum for changing the liquid toner to another one, the amount the amount of liquid toner to be supplied between the photoconductor drum and the developing roller becomes increased, so that meniscus can be quickly formed when the change of colors takes place, so that a stable environment conditions can be attained together with attaining stable developmental conditions, resulting in the improvement in the image quality.
It is preferable that after rotating the developing roller at the faster speed, the developing roller is decelerated to the rotation speed thereof at the time of the development until the development is performed.
Accordingly, after rotating the developing roller at the faster speed, the developing roller is decelerated to the rotation speed thereof at the time of the development until the development is performed. Therefore, it is possible to avoid the problem in which an unstable development is occurred by an excess supply of liquid toner between the photoconductor drum and the developing roller as a result of insufficient deceleration of the developing roller. Therefore, the decrease in printing quality can be substantially prevented.
A seventh aspect of the present invention is a printing apparatus comprising: a photoconductor drum having a surface on which an electrostatic latent image is formed; a developing roller provided in a rotatable manner such that at least the surface of the developing roller is wet with liquid toner, and developing the electrostatic latent image by supplying the liquid toner on the surface of the photoconductor drum by electrophoresis while keeping a rotary motion of the developing roller; and a control means for controlling the rotation speed of the developing roller such that the rotation speed of the developing roller before the development of the electrostatic latent image by supplying the liquid toner is faster than the rotation speed of the developing roller during the development of the electrostatic latent image.
According to this invention, the control means imparts a rotary motion of the developing roller to supply the liquid toner supplied on the surface of the developing roller to the photoconductor drum by electrophoresis. Before the development of the electrostatic latent image by supplying the liquid toner, the rotation speed of the developing roller before the development of the electrostatic latent image is faster than the rotation speed of the developing roller during the development of the electrostatic latent image. Therefore, the amount of liquid toner to be supplied between the photoconductor drum and the developing roller becomes increased, so that meniscus can be quickly formed when the change of colors takes place, so that a stable development can be attained and the image quality can be improved.
In this invention, preferably, after rotating the developing roller at the faster speed, the developing roller is decelerated to the rotation speed thereof at the time of the development until the development is performed.
Accordingly, after rotating the developing roller at the faster speed, the developing roller is decelerated to the rotation speed thereof at the time of the development until the development is performed. Therefore, it is possible to avoid the problem in which an unstable development is occurred by an excess supply of liquid toner between the photoconductor drum and the developing roller as a result of insufficient deceleration of the developing roller. Therefore, the decrease in printing quality can be substantially prevented.
In this invention, preferably, a plurality of the developing rollers is provided depending on the kinds of the liquid toner, a moving means is provided on a position where one of the plurality of the developing rollers is brought in close to the photoconductor drum to allow the formation of meniscus of the liquid toner placed between the developing roller and the photoconductor drum and another moving means is provided on a position where the developing roller is moved away from the photoconductor drum to prevent the formation of meniscus of the liquid toner, and the control means controls the rotation speed of the developing roller such that the rotation speed of the developing roller before the development of the electrostatic latent image by supplying the liquid toner after closing to the photoconductor drum by the moving means is faster than the rotation speed of the developing roller during the development of the electrostatic latent image.
In this invention, the moving means moves the developing roller away from the photoconductor drum, shifting into a state of preventing the formation of meniscus of the liquid toner placed between the developing roller and the photoconductor drum. At this time, if another developing roller corresponding to another liquid toner is brought in close to the photoconductor drum for the purpose of supplying another liquid toner, the rotation speed of the developing roller is increased until the development is performed. Thus, the rotation speed of the developing roller before the development of the electrostatic latent image is faster than the rotation speed of the developing roller during the development of the electrostatic latent image. In the case of using several kinds of liquid toners in the development, meniscus of each liquid toner can be quickly formed when the change of colors takes place. Thus, a stable environment conditions can be attained together with attaining stable developmental conditions, resulting in the improvement in the image quality. In addition, these liquid toners are hardly mixed, so that excellent multi-color printing can be performed without causing undesired mixing of colors, adapting to better meet various customers"" needs.